1. Field of Invention
The present invention relates to a selectively one-way wrench and, more particularly, to a selectively one-way wrench for firm engagement with a screw or nut when rotated in a direction and for quick release of the screw or nut when rotated in an opposite direction.
2. Related Prior Art
A one-way wrench is used to rotate a screw or nut in a first direction and release the screw or nut when the one-way wrench is rotated in a second direction opposite to the first direction. Typically, the one-way wrench includes at least one claw biased to a toothed wheel by a spring. The toothed wheel includes a driving portion for engagement with the screw or nut. As the one-way wrench is rotated in the first direction, the spring causes the claw to engage with and rotates the toothed wheel so that the one-way wrench rotates the screw or nut. As the one-way wrench is rotated in the second direction, the spring allows the claw to rattle and move on the toothed wheel so that the one-way wrench does not rotate the screw or nut.
As disclosed in U.S. Pat. No. 6,691,594, a selectively one-way wrench includes a switch operable to cause a spring to bias a selected one of two claws into engagement with a toothed wheel. As the selectively one-way wrench is rotated in a first direction, the spring causes the claw to engage with and rotates the toothed wheel so that the one-way wrench rotates the screw or nut. As the selectively one-way wrench is rotated in a second direction opposite to the first direction, the spring allows the claw to rattle and move on the toothed wheel so that the one-way wrench does not rotate the screw or nut. In practice, in the rotation in the second direction, the selected claw continues to engage with the toothed wheel for a short period of time before the selected claw actually leaves the toothed wheel. That is, the selective-one way wrench continues to rotate the screw or nut for an angle in the beginning of the rotation in the second direction. Such angle has been proven to be big enough to render the selectively one-way wrench substantially useless in a narrow space.
To solve the foregoing problem, Chinese Patent No. 101293340 discloses a selectively one-way wrench that includes a biasing unit that includes two springs 14 and 22. The first spring 14 pushes a claw 16 from a claw 18. The second spring 22 biases the claw 16 or 18 into engagement with a toothed wheel 20 and keeps the claw 16 or 18 extend co-centrally with the toothed wheel 20. The second spring 22 is a V-shaped leaf spring formed with an apex 22c and two ends 22d. The apex 22c must be inserted in a corner 38a of a wall 38 of a head to allow insertion of at least one of the ends 22d in a slit made in the head to prevent the second spring from sliding in the head. However, it requires precision in selecting the springs 14 and 22.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.